This testosterone level thing is such a furphy. Female weightlifters and powerlifters who take PEDs get very strong, but even the strongest don’t out lift the strongest men.
Anecdotal example. I had a male friend who was basically my age and height. So below average height for a man, even though I’m above average height for a woman.
He discovered that he had really, really low testosterone levels and needed to supplement them. Even before the supplements he was way stronger than I am. His strength advantage didn't disappear with his testosterone - because he still had all the other advantages of a male body.
Perhaps a young boy who starts on puberty blockers prior to puberty and goes straight on to female sex hormones might not have all those advantages, although they’d still have some.
I’d suspect though, that such a boy would have a range of health issues, physical, mental and neurological, which would preclude them from sport at any advanced level.